The present invention relates to electrical motors and is particularly applicable but not limited to methods and devices for detecting malfunctions in an electrical stepper motor.
The ubiquity and popularity of lottery games is undisputed. Everyday numerous people in different countries buy lottery tickets in the hope of striking it rich. Arguably, the most popular form of such lotteries, and certainly the one with the largest payoffs, is the game of Lotto, typically sold through an electronic online lottery system. For this type of a lottery, for each wager, a player selects a predetermined number of numerals from a finite pool of choices. A draw is then performed during which the same predetermined number of numerals are randomly selected from the pool of choices. Depending on the number of matches between a player""s selected numerals and the randomly selected numerals, the player wins prizes.
For a game as outlined above, a database of numbers selected by players is created and, for each wager, a player is provided with a ticket. The ticket has printed on it not only the amount of the wager but also the sets of numerals selected by the player. The ticket then becomes the player""s proof that he made a wager and what numerals he wagered on. Another important part of the ticket, aside from the numerals selected by the player, is the ticket""s identifying number. This identifying number correlates to a record at the lottery central system that contains the details about that particular ticket.
Clearly, the printing of the lottery ticket, usually done at the point of sale terminal, is important. It is for this reason that the ticket printers need to have some way of determining whether a print job has been completed or not. Since each ticket constitutes a print job, a successful print job means that a particular ticket has validly been printed and, as such, the record for that printed ticket is valid. The valid record can then be added to the records which will be checked against the winning numbers.
Unfortunately, malfunctions in the printer, and specifically printer jams, can cause trouble. A printer jam does not necessarily stop the printer from printing. Instead, in one type of printer jam, the printer head may continue to print with the paper not being fed properly. This leads to the data destined for a whole ticket or tickets to be printed on a single line on the paper. Such a condition is usually not automatically reported to the lottery central system so that when a printer paper feed jams, the print head continues to print and the lottery ticket terminal, and hence the lottery central system, is under the impression that tickets are being printed. While this does not affect the entry and storage of valid records, there is no corresponding evidence of a valid ticket being printed. The player does not have any proof of his or her wager as the ticket has been misprinted due to the printer jam. While the above scenario describes a paper feed problem, other printer jam scenarios which lead to the misprinting of tickets are possible.
One attempt to solve the above problem of tracking the paper feed in the printer and reporting any errors when they occur involved the use of special paper. This approach used specially printed paper with regularly spaced dots or other marks printed on the back of the paper. An optical scanner capable of detecting the marks determined the speed of the paper feed by counting the number of marks detected for every given period of time. When the speed fell below a certain threshold, there was, in all probability, a paper jam. While this approach works, it cannot be easily adapted to different types of printers as it requires not only specialized paper but also specialized hardware including at least one optical sensor to detect the marks on the paper.
Based on the above, there is a need for a solution that can easily be built into printers and which does not require special paper.
It is therefore an object of the present invention to at least mitigate if not overcome the shortcomings of the prior art.
The present invention relates to methods, devices and circuits for detecting malfunctions in stepper motors. A driver circuit driving a stepper motor produces a signal proportional to the current in the windings of the stepper motor. This signal is then amplified and integrated for ease of comparison. The resulting signal is then compared to a specific entry in a table of values with each entry in the table corresponding to an operating profile of the stepper motor. If the resulting signal does not correspond to the operating profile for which the motor is configured, the stepper motor is jammed or stalled. A suitable alarm and a corresponding sequence of actions may then be triggered.
In a first aspect the present invention provides a method for detecting a specific condition in a device having an electric motor, the method comprising:
a) determining a signal level for at least one winding of said motor;
b) comparing said signal level to a predetermined expected signal level range; and
c) generating an alarm relating to said specific condition in said device in the event said signal level is not within said predetermined expected signal level range.
In a second aspect the present invention provides a circuit for detecting malfunctions in a device having an electric motor, the circuit comprising:
feedback circuit means for retrieving a feedback signal related to a signal in at least one winding in said motor;
comparing circuit means for comparing said feedback signal with an expected signal level range,
wherein a malfunction is detected when said feedback signal is not within said expected signal level range.
In a third aspect the present invention provides a system for detecting malfunctions in a motor, the system comprising:
processing means for comparing a feedback signal with an expected signal level range;
motor driver means for driving said motor and for producing said feedback signal, said feedback signal being related to a current level in at least one winding of said motor,
wherein said feedback signal is received by said processing means from said motor driver means and a malfunction is detected when said feedback signal level is not within said expected signal level range.